AsyncCompletedEventArgs.Cancelled Properti

  • Referensi

Definisi

Ruang nama:
System.ComponentModel
Rakitan:
System.ComponentModel.EventBasedAsync.dll
Rakitan:
System.dll
Rakitan:
netstandard.dll
Sumber:
AsyncCompletedEvent.cs
Sumber:
AsyncCompletedEvent.cs
Sumber:
AsyncCompletedEvent.cs

Mendapatkan nilai yang menunjukkan apakah operasi asinkron telah dibatalkan.

public:
 property bool Cancelled { bool get(); };
public bool Cancelled { get; }
member this.Cancelled : bool
Public ReadOnly Property Cancelled As Boolean

Nilai Properti

Boolean

true jika operasi latar belakang telah dibatalkan; jika tidak false. Default adalah false.

Contoh

Contoh kode berikut menunjukkan penggunaan AsyncOperation untuk melacak masa pakai operasi asinkron. Contoh kode ini adalah bagian dari contoh yang lebih besar yang disediakan untuk System.ComponentModel.AsyncOperationManager kelas .

using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Globalization;
using System.Threading;
using System.Windows.Forms;

Imports System.Collections
Imports System.Collections.Specialized
Imports System.ComponentModel
Imports System.Drawing
Imports System.Globalization
Imports System.Threading
Imports System.Windows.Forms

// This event handler updates the ListView control when the
// PrimeNumberCalculator raises the CalculatePrimeCompleted
// event. The ListView item is updated with the appropriate
// outcome of the calculation: Canceled, Error, or result.
private void primeNumberCalculator1_CalculatePrimeCompleted(
    object sender, 
    CalculatePrimeCompletedEventArgs e)
{
    Guid taskId = (Guid)e.UserState;

    if (e.Cancelled)
    {   
        string result = "Canceled";

        ListViewItem lvi = UpdateListViewItem(taskId, result);

        if (lvi != null)
        {
            lvi.BackColor = Color.Pink;
            lvi.Tag = null;
        }
    }
    else if (e.Error != null)
    {
        string result = "Error";

        ListViewItem lvi = UpdateListViewItem(taskId, result);

        if (lvi != null)
        {
            lvi.BackColor = Color.Red;
            lvi.ForeColor = Color.White;
            lvi.Tag = null;
        }
    }
    else
    {   
        bool result = e.IsPrime;

        ListViewItem lvi = UpdateListViewItem(
            taskId, 
            result, 
            e.FirstDivisor);

        if (lvi != null)
        {
            lvi.BackColor = Color.LightGray;
            lvi.Tag = null;
        }
    }
}

' This event handler updates the ListView control when the
' PrimeNumberCalculator raises the CalculatePrimeCompleted
' event. The ListView item is updated with the appropriate
' outcome of the calculation: Canceled, Error, or result.
Private Sub primeNumberCalculator1_CalculatePrimeCompleted( _
    ByVal sender As Object, _
    ByVal e As CalculatePrimeCompletedEventArgs) _
    Handles primeNumberCalculator1.CalculatePrimeCompleted

    Dim taskId As Guid = CType(e.UserState, Guid)

    If e.Cancelled Then
        Dim result As String = "Canceled"

        Dim lvi As ListViewItem = UpdateListViewItem( _
            taskId, _
            result)

        If (lvi IsNot Nothing) Then
            lvi.BackColor = Color.Pink
            lvi.Tag = Nothing
        End If

    ElseIf e.Error IsNot Nothing Then

        Dim result As String = "Error"

        Dim lvi As ListViewItem = UpdateListViewItem( _
            taskId, result)

        If (lvi IsNot Nothing) Then
            lvi.BackColor = Color.Red
            lvi.ForeColor = Color.White
            lvi.Tag = Nothing
        End If
    Else
        Dim result As Boolean = e.IsPrime

        Dim lvi As ListViewItem = UpdateListViewItem( _
            taskId, _
            result, _
            e.FirstDivisor)

        If (lvi IsNot Nothing) Then
            lvi.BackColor = Color.LightGray
            lvi.Tag = Nothing
        End If
    End If

End Sub

Keterangan

Cancelled Ketika properti adalah true, operasi asinkron terganggu.

Delegasi penanganan aktivitas aplikasi klien harus memeriksa Cancelled properti sebelum mengakses properti apa pun di kelas yang berasal dari AsyncCompletedEventArgs; jika tidak, properti akan menaikkan InvalidOperationException jika operasi asinkron terganggu.

Catatan Bagi Inheritor

Jika Anda menyediakan properti baca-saja di kelas turunan, pastikan untuk memanggil RaiseExceptionIfNecessary() metode . Ini mencegah klien mengakses properti yang berpotensi tidak valid karena kegagalan dalam operasi asinkron.

Berlaku untuk

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